title: A comparison of the thermal-dose equation and the intensity-time product, Itm, for predicting tissue damage thresholds.
abstract: Thermal dose is the most generally accepted concept for estimating temperature-related tissue damage thresholds in high-intensity focused ultrasound (HIFU) procedures. However, another approach based on the intensity-time product I t(m) =D has been used, where D is a tissue-dependent damage threshold, I is the spatial-peak, temporal-average intensity and t is time. In this study, these two approaches were compared analytically by substituting a well-known soft-tissue solution for temperature vs. time into the thermal dose equation. From power law fits of I vs. t, m was found to fall between about 0.3 and 0.8. In terms of the intensity required for cell death for a given exposure time, the standard deviation of the error between the full thermal-dose formulation and the I t(m) =D prediction based upon the power-law fit was less than 5% for focal beam diameters up to 3 mm. Thus, for the practical range of HIFU parameters examined, the intensity-time product relationship is equivalent to the thermal dose formulation.
authors.affiliation: U.S. Food and Drug Administration, Center for Devices and Radiological Health, Silver Spring, MD 20993-0002, USA. gerald.harris@fda.hhs.gov
authors.forename: Gerald R
authors.initials: GR
authors.lastname: Harris
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Herman
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Myers
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000502:physiology* / Q000528:radiation effects*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D006801:Humans; D008954:Models, Biological; D011829:Radiation Dosage; D013813:Therapy, Computer-Assisted / Q000379:methods*